1. Technical Field
Embodiments of the present invention relate to a cavity filter, more particularly to a mixed-mode cavity filter in which different modes are combined.
2. Description of the Related Art
Advances in communication services lead to increased transmission speeds, which in turn require increases in system bandwidth, improved reception sensitivity, and minimized interference from carriers of other communication systems.
As such, there is a growing demand for a broadband filter that offers low insertion loss and high rejection. Also, in order to prevent loss in transmission power and decreases in reception sensitivity due to a base station's power feed cables, most RF units are being installed directly below the base station antenna; a few examples including the tower mounted amplifier (TMA), the remote radio head (RRH), and the radio integrated antenna (RIA).
Due to the characteristic of being installed directly below the antenna, an RF unit is required to have a small size and a light weight. Thus, there is active research under way aimed at reducing the size of the filter, which accounts for a large part of the unit's weight and size.
Dielectric resonators can provide low insertion loss properties, but relatively larger sizes and higher costs may be required. Metal coaxial resonators can provide a smaller and more light-weight filter, but may be subject to high losses.